"Zalman's CNPS9900DF heatsink is a twin tower cooler that stands 154mm tall and is built around three 6mm diameter composite wick copper heatpipes. For a look inside a composite wick heatpipe, check this out. The CNPS9900DF comes with two fans, a 120mm intake fan that runs at a fixed speed of 1000RPM and a center, 135mm PWM fan than operates at 1400-900RPM. "